In many places, the Wind blows quite steadily from a predictable direction during a certain part of the day. For instance, in Southern California near the ocean the wind will blow in from the west to fill in the vacuum left by the land-heated thermally rising air ashore.
Once the sail is set a mobilist may go along the shore for many miles, in a generally north or south direction. He may also turn the windmobile around and go in the opposite direction, if he has a device that will allow him to this, while still adhering to the physical laws that govern a windmobile.